Method of determining quantization parameters

1. A method of determining quantization parameters, comprising: receiving a block of image data; calculating a first variance of the block of image data; calculating a second variance of the block of image data by subtracting an image moment of the block of image data from the first variance; and determining a quantization parameter for the block of image data according to the second variance; wherein the image moment reflects an image gradient in the block of image data.

2. The method of claim 1 , wherein the second variance is an average of difference values of the block of image data correlated to a mathematical function other than a mean of the block of image data.

3. The method of claim 2 , wherein the mathematical function is a minimum mean square error estimator of the block of image data.

4. The method of claim 1 , wherein the step of calculating the second variance of the block of image data by subtracting the image moment of the block of image data from the first variance comprises: subtracting a first raw image moment along a first direction multiplied by a first moment parameter and a second raw image moment along a second direction multiplied by a second moment parameter from the first variance, to obtain the second variance.

5. The method of claim 4 , further comprising: setting values of the first moment parameter and the second moment parameter to control a correlation of an image gradient in the block of image data with the quantization parameter.

6. The method of claim 5 , wherein the block of image data is an N×N block, and each of the values of the first moment parameter and the second moment parameter is within a range from 0 to m, wherein m is equal to: m = 3 ⁢ N 2 N 2 - 1 .

7. The method of claim 5 , wherein each of the values of the first moment parameter and the second moment parameter is within a range from 0 to 3.

8. The method of claim 1 , further comprising: determining that the quantization parameter for the block of image data has a first value when the second variance has a first value; and determining that the quantization parameter for the block of image data has a second value smaller than the first value of the quantization parameter when the second variance has a second value smaller than the first value of the second variance.

9. A method of determining quantization parameters, comprising: receiving a block of image data; calculating a second variance of the block of image data by using an image moment of the block of image data; and determining a quantization parameter for the block of image data according to the second variance; wherein the image moment reflects an image gradient in the block of image data.

10. The method of claim 9 , wherein the second variance is an average of difference values of the block of image data correlated to a mathematical function other than a mean of the block of image data.

11. The method of claim 10 , wherein the mathematical function is a minimum mean square error estimator of the block of image data.

12. The method of claim 9 , wherein the step of calculating the second variance of the block of image data by using the image moment of the block of image data comprises: calculating a first variance of the block of image data; and subtracting a first raw image moment along a first direction multiplied by a first moment parameter and a second raw image moment along a second direction multiplied by a second moment parameter from the first variance, to obtain the second variance.

13. The method of claim 12 , further comprising: setting values of the first moment parameter and the second moment parameter to control a correlation of an image gradient in the block of image data with the quantization parameter.

14. The method of claim 13 , wherein the block of image data is an N×N block, and each of the values of the first moment parameter and the second moment parameter is within a range from 0 to m, wherein m is equal to: m = 3 ⁢ N 2 N 2 - 1 .

15. The method of claim 13 , wherein each of the values of the first moment parameter and the second moment parameter is within a range from 0 to 3.

16. The method of claim 9 , further comprising: determining that the quantization parameter for the block of image data has a first value when the second variance has a first value; and determining that the quantization parameter for the block of image data has a second value smaller than the first value of the quantization parameter when the second variance has a second value smaller than the first value of the second variance.